The invention provides a method of minimizing oil consumption in a gas turbine engine. In general, oil is consumed as a consequence of air flow into the engine oil circuit to create a vacuum condition in the bearing oil chambers, thus preventing oil leakage into the compressed air and gas path of the engine. Since air is drawn into the bearing chambers to oppose oil leakage flow and the air mixes with the oil, an oil-air separator is necessary to reconstitute the oil and exhaust the air. Oil is consumed in that the air exhausted from the oil-air separator contains oil residue in an aerosol form. This conventional design inevitably consumes a portion of the oil which must be made up from oil supplies in the oil circuit. Oil aerosols have been the cause of increased level of engine emissions and staining of the engine nacelle surfaces.
A typical gas turbine engine includes an oil circuit that supplies cooling and lubricating oil to a number of bearings that support the engine shafts at longitudinally spaced apart supports along the shaft axis. The bearing chambers enclose the bearings and maintain a volume of oil with an oil-air interface in communication with the volume of oil enclosed within the bearing chamber. Within the bearing chambers, oil is supplied under pressure from an oil supply conduit and is sprayed at selected areas of bearing or is diffused through bearing surfaces. Oil flow simultaneously cools the bearings which develop heat under friction, lubricates the bearings, flushes out any foreign particles that develop and splashes within the bearing chamber to cool and lubricate internal surfaces before being withdrawn from the bearing chamber under the vacuum of a scavenge pump. Depending on the engine design, various oil circulation mechanisms are provided in flow communication with each bearing chamber for supplying a continuous flow of oil to the bearing chamber inlet and for evacuating or scavenging spent oil from an outlet of the bearing chamber.
As mentioned above, typically the bearing chambers of gas turbine engines utilize carbon seals or labyrinth seals that prevent escape of oil from the bearing chamber by creating a vacuum condition within the bearing chamber relative to the ambient engine conditions. Compressed air external to the bearing chamber is allowed to pass through the bearing chamber seals into the bearing chamber creating a flow of air that counteracts any tendency for the oil to escape. When the engine is at rest, the oil is maintained within the bearing chamber simply by friction between sealing faces of the prior art seals that are generally friction seals, carbon seals or labyrinth seals depending on the particular application. In all cases however, airflow across the sealing surfaces is provided to create a vacuum condition within the bearing chamber relative to ambient engine condition and provide an airflow across the sealing surface to prevent the escape of oil from the bearing chamber enclosing the oil lubricating and cooling the bearings.
Examples of prior art seals are shown in: U.S. Pat. No. 5,582,413 to Lendway that provides an oil seal for a gas turbine with radially grooved seal surface; U.S. Pat. No. 5,813,830 to Smith et al. showing a carbon seal contaminant barrier system for a gas turbine engine; and U.S. Pat. No. 5,174,584 to Lahrman for fluid bearing face seal for gas turbine engines with spring loaded sealing ring. Of particular interest to the present invention is the development of hydropad seals as shown for example in U.S. Pat. No. 6,257,581 B1 to Flaherty et al. for an aerospace housing and shaft assembly sealed with hydropad seals.
It is an object of the present invention to minimize or substantially reduce the consumption of oil in a gas turbine engine by avoiding reliance on air intake into the engine oil circuit bearing chambers for sealing purposes.
It is a further object of the invention to provide a method of substantially reducing oil consumption and resultant disadvantages of entraining air into the oil which is circulated through the engine including avoiding the need for an oil/air separator, reduction of oil loss through exhausted aerosols from the oil/air separator, reduction in pump size, reduction in heat input into the oil circuit, oil tank size and oil cooler size due to the volume reduction in the oil/air mixture.
Further objects of the invention will be apparent from review of the disclosure, drawings and description of the invention below.